Need some help......What could it be, vacuum leak or timing off a tooth

IMO, it's possible that both codes are related. Suggest focus on the P0203 DTC as this could easily cause the P0303 DTC.

The P0203 could be a bad fuel injector, bad/loose connector, wiring harness fault, or bad PCM injector driver.

To rule in/out a bad fuel injector, either swap with another cylinder or use an injector cleaning/flow test service such as injectorrx.com.

Once the injectors are confirmed good, inspect all connectors. Look for bent/pushed pins. Check that the connectors are fully inserted.

The next step involves testing the resistance of the wiring harness between the injector connector and the PCM connector. It will be necessary to remove the PCM for this step. If there is a problem in the wiring harness, it will have to be tracked down and resolved.

Since this is a recent motor swap, the possibility of wiring harness damage should be considered.

If the wiring harness is OK, then it is likely that the PCM is bad.

IMO, the bogging at low RPM is a combination of the PI swap and the misfire. If this were my car, I would not pay any attention to the bogging symptom until the motor runs DTC free.

The problem only showed immediately up after I replaced the timing chain tensioners and arms. Can anyone confirm if counting the links ensured everything is set up correctly and I should rule out timing issues?

Also is the cam sensor supposed to line up at TDC?

I checked all injectors and they check out OK. (they all have 12V, fluctuating voltage testing the ground trigger and all resistance readings are the same.

I used a spark tester on all coils and they all have spark.

The MAF sensor signal voltage fluctuated consistently with increased idle.

I haven't run a compression check yet.

Any thoughts? I keep thinking I screwed up the timing, but I didn't take the chain off, didn't feel the need to use cam holding tools and I counted the links multiple times.

I checked the compression and all cylinders are within 5% of each other. Now I'm getting codes P0203, P0303, P0300.

Anyone have any ideas?

Maybe you've got a bum injector. Use an automotive stethoscope (or a long screwdriver with the blunt end on your ear) and listen to the #3 fuel injector at idle. You should hear it clicking. Compare the sound to the injectors next to it.

You might try swapping the injector on #3 with the one on, say, #2 and see if the codes follow the injector or stay with the cylinder.

BTW, when you got the new engine, did you have to do anything to the front cover or specifically the crank damper/pulley? If so, did you properly torque the crankshaft bolt?

Hey guys I actually have a 94 Thunderbird that i have converted to the mustang setup on the motor for performance reasons.

I installed pi heads with the stock mustang cams. the car now runs ok at idle cold, but cannot go higher than 3k rpm when snapping the throttle. with the engine at operating temp it idles poorly with intermittent miss but operates fine at high idle, and stalls when the throttle is released.

i have checked and verified the correct adjustment and operating of - tps, iac, and mas.

the engine also backfired on me once while stumbling at 3k rpm. was wondering about the possibility of incorrect cam timing. also wondering if it could be an ecm incompatibility due to the change in cam lobe duration. I haven't tried the compression test yet but good idea.

any advice would be appreciated

Stock Mustang cams have nowhere near enough duration or overlap to confuse a stock PCM.

Backfiring, poor running and so on after the work you did suggests to me that there may well be a timing issue with one or both banks. Next step I'd take is a compression test.

trinity_gt said:

Stock Mustang cams have nowhere near enough duration or overlap to confuse a stock PCM.

Backfiring, poor running and so on after the work you did suggests to me that there may well be a timing issue with one or both banks. Next step I'd take is a compression test.

Click to expand...

Thank you.

trinity_gt said:

Stock Mustang cams have nowhere near enough duration or overlap to confuse a stock PCM.

Backfiring, poor running and so on after the work you did suggests to me that there may well be a timing issue with one or both banks. Next step I'd take is a compression test.

Click to expand...

What kind of variance could i expect between banks if the timing is correct?

All else being equal all cylinders should be within 10% or so of each other.

If one cylinder is down a bit you might have a burnt valve or a broken ring or land. If one bank is down (and all cylinders on that bank read reasonably similar) it's likely a cam timing issue.